The invention relates to novel compositions curable to transparent, oxygen permeable polysiloxane resins. The cured resins are hydrophilic and inherently wettable by human tear fluid because they contain a specific-type and an effective amount of certain acrylate-functional siloxane units to provide a certain degree of surface wettability. This invention specifically relates to hydrophilic inherently wettable optical devices such as eye contact or intraocular lenses manufactured from such resins.
Oxygen permeable, hard silicone (polysiloxane) resin optical devices manufactured from phenyl-containing polysiloxane resins are described in U.S. Pat. No. 4,198,131 to Birdsall, et al. (issued Apr. 15, 1980) which is hereby incorporated by reference. Silicone materials can possess a high degree of oxygen permeability and this property makes such materials highly desirable for use as eye contact lenses. Hard silicone resin contact lenses of the Birdsall, et al. type are also desirable for the correction of significant amounts of astigmatism because the hard lens does not conform to the shape of the cornea in the manner that soft contact lenses typically do. The silicone resin materials taught by Birdsall, et al. have a disadvantage in that the surfaces of such silicone resins are not considered to be inherently wettable by water or by human tear fluid.
Human tear fluid contains mucus and other components which tend to render surfaces to which the tear fluid is exposed more wettable by the aqueous tear fluid than by water alone. Thus, a material which may only be marginally wettable by water may be completely wetted by human tear fluid and would therefore be useful as, for example, a corneal contact lens material without further modification. The composition of human tear fluid varies from person to person and may even vary from day to day for the same person depending upon the general health of the individual. Thus, individuals will vary in their ability to have their tear fluid "wet" the surface of a contact lens and it must be recognized that what may be an "inherently wettable" contact lens for some individuals may not be "inherently wettable" for others. The Birdsall, et al. patent states that in order for the lens to perform well in the eye, it must be made "hydrophilic" and that can be accomplished by means of the Gesser, et al. plasma treatment process of U.S. Pat. No. 3,925,178 (issued Dec. 9, 1975) or by some other standard technique.
The terms "hydrophilic" and "hydrophobic" are often used in the field of eye contact lenses to describe the surface wettability of the devices, but those terms have been given many meanings. As noted above, individuals vary in their ability to wet the surfaces of eye contact lenses, so the best way to define a material which is "inherently wettable by human tear fluid" for the purposes of this invention appears to be to define a "hydrophilic" cured polysiloxane resin as being one which possesses an advancing water-in-air contact angle of no greater than 80.degree. at room temperature (21.degree..+-.2.degree.) while a "hydrophobic" cured polysiloxane resin is defined to be one which possesses an advancing water-in-air contact angle of greater than 80.degree. at room temperature. The contact angle measurements are made using distilled water on the surface of a disk of resin or a resin lens which has been equilibrated (hydrated) with an aqueous liquid such as water or isotonic saline. The preferred method for obtaining a hydrated disk of resin or resin lens surface involves heating the article in distilled water or aqueous isotonic saline solution to about 80.degree. C. for about 15 to 30 minutes in one of a number of well known and commercially available eye contact lens heat disinfector (aseptor) units used to sterilize eye contact lenses. Thus, if a biocompatible polysiloxane lens material as described herein is found to be "hydrophilic", this is taken to mean that it is reasonable to go further and to empirically confirm that the material possesses an effective amount of acrylate-functional siloxane units such that its surfaces are "inherently wettable by human tear fluid" for the purposes of this invention. This can be done by inserting a sterile, hydrated lens manufactured from that resin material to the wearer's prescription on the corneae of several patients. The surface of the lens is visually observed after placement on the eye to ascertain whether or not the lens surface either is capable of holding a precorneal tear film for a period of time that is at least equal to 4 to 5 seconds--which corresponds to the average time between consecutive blinks of a human eye, i.e., about 12 blinks per minute--or possesses a lens front surface tear film evaporation time of at least 10 seconds when the eye is held open after a continuous tear film has formed over the front surface. If either of the latter two empirical observations are met and the wearer has an acceptable level of visual acuity, then the lens material is deemed to be "inherently wettable by human tear fluid" for that wearer for the purposes of this invention.
The surface treatment hydrophilization process of Gesser, et al. renders the Birdsall, et al. polysiloxane resins wettable to a short depth from the lens surface and thereby capable of being worn, but it leaves the underlying substrate hydrophobic. That is a disadvantage because in the event that the contact lens should become scratched or if an eye care practitioner should later desire to reshape the lens to better conform the lens to the wearer's eye by reshaping the surface, such occurrences can result in exposure of the hydrophobic substrate and necessitate another surface treatment to again make the lens wettable and suitable for wear. Prior to surface treatment, a phenylpolysiloxane resin of the Birdsall, et al. type was found to have an advancing water-in-air contact angle of greater than 100.degree. both before and after hydration.
Hard contact lenses manufactured from polymethylmethacrylate alone can be tolerated in the eye for reasonably long periods of time (reported "water" contact angles range from about 55.degree.-65.degree.), but this very well known organic hard contact lens material is not considered to be oxygen permeable and is sometimes referred to in the literature as being a hydrophobic material. Other organic monomers such as 2-hydroxyethyl methacrylate which contain hydrophilic hydroxyl groups can be employed to impart inherent and/or increased wettability to hard organic contact lens materials since the hydrophilic groups are dispersed throughout the polymeric lens material. However, such hard materials do not possess the oxygen permeability obtainable from silicone materials of the Birdsall, et al. type.
In an attempt to obtain a hard contact lens material that rivalled the oxygen permeability of the silicone materials and was also inherently wettable, eye contact lenses made from copolymers of oxygen permeable siloxanyl alkyl ester monomers and less oxygen permeable organic unsaturated monomers such as esters of acrylic and methacrylic acid have been taught such as those found in U.S. Pat. Nos. 3,808,178 (Gaylord, issued Apr. 30, 1974), 4,120,570 (Gaylord, issued Oct. 17, 1978) and 4,152,508 (Ellis, et al., issued May 1, 1979). Tanaka, in U.S. Pat. No. 4,235,985 (issued Nov. 25, 1980), teaches the use of hydrophilic radicals such as hydroxyl on the organic substituents present in the acrylate-functional siloxanes to provide inherent wettability. Copolymers of a polymerized reactive organosilane such as CH.sub.2 .dbd.C(CH.sub.3)COO(CH.sub.2).sub.3 Si(OCH.sub.3).sub.3 and monomeric methyl methacrylate are taught in U.S. Pat. No. 4,280,759 (Neefe, issued July 28, 1981).
Other compositions containing acrylate-functional siloxane units which are curable to resins or useful as intermediates can be seen from an examination of U.S. Pat. Nos. 2,922,806 (Merker, issued Jan. 26, 1960) and 4,035,355 (Baney, et al., issued July 12, 1977) and U.K. Patent Application GB 2,023,628 (Berg, published Jan. 3, 1980). None of these teach contact lens uses for the compositions and products described therein.
During the course of my attempts to develop an inherently wettable, highly oxygen permeable polysiloxane resin, I discovered that certain acrylate-functional polysiloxane compositions which contained at least 30 mole percent of acrylate-functional siloxane units of the unit formula H.sub.2 C.dbd.CRCOOR'SiO.sub.1.5 (R is a methyl radical or hydrogen and R' is a divalent alkylene radical of from 1 to 4 inclusive carbon atoms) could be cured alone or in the presence of certain aliphatically unsaturated organic compounds to form oxygen permeable polysiloxane or polysiloxane/organic copolymer resins which possessed water-in-air contact angles which were similar to those possessed by hard polymethylmethacrylate resins. These compositions, resins and optical devices made therefrom are the subject of U.S. patent application Ser. No. 376,450 to Darrell D. Mitchell entitled "Inherently Wettable Silicone Resin Optical Devices" that was filed on May 10, 1982 and assigned to the same assignee as the present invention (hereby incorporated by reference). In that Patent Application, a specific type of acrylate-functional siloxane unit was found to produce inherently wettable resins when at least 30 mole percent of such units were present in the polysiloxane composition. That acrylate-functional siloxane unit was used both as a reactive cross-linking agent to cure the resin and to provide wettability. The presence of additional alkyl groups bonded by means of carbon-silicon bonds to the same silicon atom bearing the acrylate-functional radical was found to result in a cured polysiloxane resin with an advancing water-in-air contact angle of greater than 80.degree., and more often, greater than 90.degree.. The same result was observed when less than 30 mole percent of the aforementioned acrylate-functional siloxane units were used to produce a cured polysiloxane resin.
All of the compositions used in the above patents and the Patent Application are generally cured in such a manner that substantially all of the aliphatically unsaturated radicals present are reacted. For example, the use of a free-radical polymerization method such as a peroxide catalyst will result in reaction with as many reactive radicals as are present in the composition assuming that a sufficient amount of peroxide is employed and that the reactive radicals are available for reaction.
The novel compositions of the present invention employ a specific type of acrylate-functional siloxane unit to render the surface of the cured composition hydrophilic and thereby inherently wettable by human tear fluid. The curing of the composition is accomplished in such a manner that the acryloxy or methacryloxy radicals found in the acrylate-functional siloxane units present in the composition remain essentially unreacted after curing and are therefore available to render the cured polysiloxane resin hydrophilic and inherently wettable. The use of the hereinafter described acrylate-functional siloxane units to provide wettability is novel.
The present invention is based upon the unexpected observation that oxygen permeable cured polysiloxane resins which possess an advancing water-in-air contact angle of no greater than 80.degree. after hydration and are inherently wettable by human tear fluid can be prepared from polysiloxane compositions possessing less than a total of 30 mole percent of acrylate-functional siloxane units of the unit formula H.sub.2 C.dbd.CRCOOR'SiO.sub.1.5 when such compositions are cured by means of a Group 8 Transition Metal catalyzed addition of .tbd.SiH radicals to aliphatically unsaturated hydrocarbon radicals attached to siloxane units other than the H.sub.2 C.dbd.CRCOOR'SiO.sub.1.5 units. As will now be described further, polysiloxane compositions containing an effective amount, generally a total of from 7 to less than 30, preferably from 10 to 20 mole percent, of such acrylate-functional siloxane units can be employed to produce inherently wettable resins, thereby leaving the resin formulator with a wider latitude for selecting other siloxane units which ultimately affect the physical properties of the cured resins. As described, infra, it was also observed that when compositions of the present invention were provided with a sufficient amount of additional .tbd.SiH polysiloxane cross-linking agent to react with all of the siloxane units bearing aliphatically unsaturated hydrocarbon radicals, including the acrylate-functional siloxane units, the advancing water-in-air contact angle was found to exceed 80.degree. after hydration. That observation is consistent with the results found in U.S. Ser. No. 376,450, above, for polysiloxane resins containing less than 30 mole percent of the above acrylate-functional siloxane units.
It is one object of this invention to provide novel compositions which are capable of being cured to transparent, oxygen permeable, hydrophilic polysiloxane resins having an advancing water-in-air contact angle of no greater than 80.degree. at 21.degree..+-.2.degree. C. after hydration.
It is another object of this invention to provide a biocompatible, hard, oxygen permeable polysiloxane resin optical device, particularly in the form of an eye contact lens, having an oxygen gas permeability coefficient of at least 2.times.10.sup.-10 (cm.sup.3.cm)/(cm.sup.2.sec.cm Hg) which results in a calculated open eye Equivalent Oxygen Performance (EOP) value of at least 3 percent at 0.1 mm thickness at 21.degree..+-.2.degree. C. which is inherently wettable by human tear fluid without any necessity for the further inclusion of a source of hydrophilic groups such as hydroxyl or poly(alkyleneoxy) groups into the formulation. Such optical devices do not require surface treatments such as plasma treatment during their manufacture to render the surfaces thereof wettable by human tear fluid. The elimination of such an extra manufacturing step results in a reduction in manufacturing costs and also enables an eye care practitioner to subsequently alter the surface of the lens without necessitating retreatment of the lens to restore its wettability by human tear fluid. These lenses can be plasma surface-treated by means of the process shown in the Gesser, et al. Patent to further improve the hydrophilicity of the lens surface. Surface-treated lenses of the present invention still possess the advantage of the high oxygen permeability of silicone resins coupled with the advantage that if the lens should be scratched or modified, the underlying substrate exposed is hydrophilic after hydration instead of being hydrophobic as is the case with lenses of the type taught in the Birdsall, et al. Patent. Lenses of the present invention require no organic comonomers which tend to reduce the oxygen permeability of the lens and can therefore possess the maximum oxygen permeability attainable with the polysiloxane components selected to prepare the curable compositions.
In a more preferred embodiment, this invention provides a hard polysiloxane resin optical device suitable for use as an extended or continuous wear eye contact lens because it possesses an oxygen gas permeability coefficient of at least 8.times.10.sup.-10 (cm.sup.3.cm)/(cm.sup.2.sec.cm Hg) which results in a calculated open eye Equivalent Oxygen Performance value of at least 10 percent at 0.1 mm thickness.